U.S. patent number 6,683,125 [Application Number 09/530,797] was granted by the patent office on 2004-01-27 for talc containing polypropylene compositions.
This patent grant is currently assigned to Borealis A/S. Invention is credited to Sveinung Aasetre, Morten Augestad, Dag T.o slashed.r.ang..
United States Patent |
6,683,125 |
Augestad , et al. |
January 27, 2004 |
Talc containing polypropylene compositions
Abstract
The present invention concerns polymer compositions and a
process for the preparation thereof. The compositions comprise a
propylene polymer nucleated with a polymeric nucleating agent
containing vinyl compound units, and 0.1 to 10% talc, calculated
from the weight of the composition, to reduce shrinkage and to
improve stiffness of the composition.
Inventors: |
Augestad; Morten (Skjelsvik,
NO), T.o slashed.r.ang.; Dag (Langesund,
NO), Aasetre; Sveinung (Stathelle, NO) |
Assignee: |
Borealis A/S (Lyngby,
DK)
|
Family
ID: |
8549900 |
Appl.
No.: |
09/530,797 |
Filed: |
June 13, 2000 |
PCT
Filed: |
November 09, 1998 |
PCT No.: |
PCT/EP98/07216 |
PCT
Pub. No.: |
WO99/24501 |
PCT
Pub. Date: |
May 20, 1999 |
Foreign Application Priority Data
Current U.S.
Class: |
524/490; 524/451;
524/515; 524/529; 524/536; 524/518 |
Current CPC
Class: |
C08F
297/083 (20130101); C08L 53/00 (20130101); C08K
3/34 (20130101); C08L 53/005 (20130101); C08K
3/34 (20130101); C08L 53/00 (20130101); C08L
53/00 (20130101); C08L 2666/02 (20130101); C08L
53/005 (20130101); C08L 2666/02 (20130101) |
Current International
Class: |
C08F
297/08 (20060101); C08F 297/00 (20060101); C08K
3/34 (20060101); C08K 3/00 (20060101); C08L
53/00 (20060101); C08L 005/01 () |
Field of
Search: |
;524/452,81,849,515 |
References Cited
[Referenced By]
U.S. Patent Documents
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4436863 |
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Albee, Jr. et al. |
4551501 |
November 1985 |
Shiga et al. |
4603174 |
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Okada et al. |
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4997872 |
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5118566 |
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Wilhelm et al. |
5462987 |
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Shinonaga et al. |
5591795 |
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0000783 |
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152701 |
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JP |
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10-36584 |
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Feb 1998 |
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JP |
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WO 92/19653 |
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WO |
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WO 92/19658 |
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WO |
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Other References
Translation of JP 10-36584 A.* .
Derwent Publications Ltd., XP-002098803, Abstract of JP 01 204947
A, Aug. 17, 1989. .
Gatcher, R. et al., "Taschenbunch der Kunststoff-Additive", 1990
Carl Hanser Verlag Munchen Wien, Germany, 3. edition, pp. 564-565;
584-585. .
EP0000783--English language Abstract. .
Masahiro Kakugo, et al., "Polypropylene Composition and Sheet
Composed of the Same" Japanese Patent No. 62-135551 (A), Jun. 18,
1987--Abstract only. .
Aida Jebens, et al., "Ethylene-Propylene Elastomers", Chemical
Economic Handbook, Feb. 2000, vol. 6, pp. 544-559..
|
Primary Examiner: Wu; David W.
Assistant Examiner: Lee; Rip A
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Parent Case Text
This application is the national phase under 35 U.S.C. .sctn. 371
of PCT International Application No. PCT/EP98/07216 which has an
International filing date of Nov. 9, 1998, which designated the
United States of America.
Claims
What is claimed is:
1. Polymer composition comprising a propylene polymer nucleated
with a polymeric nucleating agent containing vinyl compound units,
and less than 5 wt-% talc, calculated from the weight of the
composition, to reduce shrinkage and to improve stiffness of the
composition.
2. The polymer composition according to claim 1, wherein the
propylene polymer contains about 0.0001 to 1% by weight of a vinyl
compound of the formula ##STR2## wherein R.sub.1 and R.sub.2
together form a 5 or 6 membered saturated or unsaturated or
aromatic ring or rings or they stand independently for a lower
alkyl comprising 1 to 4 carbon atoms.
3. The polymer composition according to any of claims 1 or 2,
wherein said polymer nucleated with a polymeric nucleating agent
comprises a propylene copolymer containing vinyl compound
units.
4. The polymer composition according to claim 3, wherein the
propylene polymer contains units derived from cycloalkane units,
3-methyl-1-butene, styrene, p-methyl-styrene, 3-ethyl-hexane units
or mixtures thereof.
5. The polymer composition according to claim 4, wherein said
propylene polymer contains units selected from units derived from
the group consisting of vinyl cyclohexane, vinyl cyclopentane,
vinyl-2-methyl cyclohexane, vinyl norbornane and mixtures
thereof.
6. The polymer composition according to claim 1, wherein said
polymer nucleated with a polymeric nucleating agent comprises a
propylene homo- or copolymer blended with a polymeric nucleating
agent containing vinyl compound units.
7. The polymer composition according to claim 6, wherein the
nucleated propylene homopolymer component of the composition
exhibits a Melt Flow Rate (MFR.sub.2) of 0.1 to 100 g/10 min, a Tc
of over 7.degree. C. higher than the Tc of the corresponding
non-nucleated polymer, a crystallinity of over 48% and a elasticity
modulus of over 2000 Mpa.
8. The polymer composition according to claim 6, wherein said
copolymer is heterophasic and exhibits a tensile modulus of over
1500 MPa and a heat deflection temperature (HDT) of over
106.degree. C.
9. The polymer composition according to claim 1, comprising 1 to
less than 5 wt-% talc and exhibiting a 10% lesser shrinkage than
the corresponding composition not containing talc.
10. The polymer composition according to claim 1, comprising 1 to
less than 5 wt-% talc and exhibiting a 12% to 20% lesser shrinkage
than the corresponding composition not containing talc.
11. A method for manufacturing polymer articles comprising
subjecting the polymer composition of claim 1 to blow moulding,
thermoforming moulding, injection moulding, compression moulding,
sheet or film extrusion or pipe or cable extrusion to obtain an
article.
12. The method according to claim 11, wherein said article is a
pipe or fitting for non-pressure sewage or pressure
applications.
13. The method according to claim 11, wherein a polymerized vinyl
compound in said polymer composition is less than 0.01 wt-% and
wherein said article is a buffer tube for optical fiber cables.
14. A process for preparing a polymer composition comprising a
propylene polymer nucleated with a polymeric nucleating agent
containing vinyl compound units and exhibiting reduced shrinkage
and improved stiffness, characterized by blending the propylene
polymer with less than 5 wt-% talc, calculated from the weight of
the composition.
15. The process according to claim 14, wherein the propylene
polymer is blended with 0.5 to less than 5 wt-% of talc.
16. The process according to claim 14 or 15, wherein talc is used
having a particle size destribution of 0.1-10 .mu.m.
17. The process according to claim 14, wherein 1 to less than 5
wt-% talc is blended with the propylene polymer nucleated with a
polymeric nucleating agent containing vinyl compound units to
provide a composition exhibiting a 10% lesser shrinkage than the
corresponding composition not containing talc.
18. The polymer composition according to claim 14, wherein the
propylene polymer is blended with 1 to less than 5 wt-% of
talc.
19. The process according to claim 14, wherein 1 to less than 5
wt-% talc is blended with the propylene polymer nucleated with a
polymeric nucleating agent containing vinyl compound units to
provide a composition exhibiting 12% to 20% lesser shrinkage than
the corresponding composition not containing talc.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polymer compositions. In
particular, the present invention concerns compositions of
efficiently nucleated copolymers. The invention further concerns a
process for preparing such compositions. Finally, the present
invention relates to the use of the new propylene polymers or
copolymers for the manufacture of products by, e.g., blow moulding,
thermoforming, injection moulding and sheet or film extrusion.
2. Description of Related Art
Propylene (PP) homo- and copolymers have excellent resistance to
heat and chemicals as well as attractive mechanical properties,
such as stiffness and impact resistance. However, processing of
polypropylene by,.e.g., injection moulding, thermoforming or blow
moulding, to form thin-walled containers has resulted in products
having insufficient transparancy. This is caused by the
semi-crystalline nature of polypropylene which leads to hazy
quality end-products.
In the prior art it has been proposed to improve the transparency
of blow moulded polypropylene by blending the polymer with various
nucleating agents such as dibenzilidene sorbitol (DBS) or
di(alkylbenzilidene)sorbitol. These traditional nucleating agents
tend to bleed out from the polymer composition during processing
and many of them give rise to fumes with an offensive smell. As a
solution to these problems, it has been suggested in the art to use
vinyl compounds, such as polymers of vinyl cycloalkanes and
3-methyl-1-butene, as nucleating agents in the form of propylene
copolymers or polypropylene compounds, cf. EP Patent Specifications
Nos. 0 152 701, 0 151 883, 0 368 577 and 0 417 319. However,
studies done on these higly nucleated materials shows that,
although their processing properties are excellent, shrinkage
increases with increasing freezing point. Further, even though
improved, the freezing point and stiffness of the polymer resins
are still too low for many applications.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate the problems
related to the prior art and to provide a novel propylene polymer
or copolymer composition having improved mechanical properties and
therefore highly suited to the manufacture of moulded products.
A second object of the invention is to provide a novel process for
preparing novel propylene copolymer compositions of the above
kind.
It is still a further object of the present invention to provide
moulded or extruded products comprising propylene copolymer
compositions.
These and other objects, together with the advantages thereof over
known processes and products, which shall become apparent from the
specification which follows, are accomplished by the invention as
hereinafter described and claimed.
The invention is based on the idea of employing talc as a
shrinkage-reducing ingredient in propylene compositions, in
particular in compositions containing propylene exhibiting a high
degree of crystallinity and a high temperature of
crystallization.
The use of talc in efficiently nucleated propylene compositions is
known in the art. Thus, EP Patent Specification No. 0 152 701
discloses blending proplyene copolymer containing poly(vinyl
cycloalkane) with a filler such as mica or talc. No examples of any
kind of compositions containing talc are given nor does the
specification give any concentration ranges for mica or talc.
Considering the fact that talc is used as a filler, it would appear
that amounts of several tens of percents have been
contemplated.
Talc is also a well-known nucleating agent. EP Patent Application
No. 0 586 109 describes a polypropylene composition containing
0.0001 to 1 part by weight of a crystal nucleating agent, such as
talc. In the examples, the amount of talc is 0.2 parts by
weight.
No indication of any beneficial effect of talc on the shrinkage of
the polypropylene composition can be found in the above
documents.
According to the present invention it has now been found that
surprisingly good mechanical results are obtained by blending talc
with propylene polymers which have been nucleated with a
polymerized vinyl compound in amounts sufficient to obtain an
increase of stiffness while reducing shrinkage to an acceptable
level. Preferably 0.1 to 10 wt-% of talc is used. Surprisingly,
although the stiffness of polypropylene nucleated with a
polymerized vinyl compound is similar to that of polypropylene
nucleated with 0.5% talc, the stiffness of the former will increase
more than of the latter when both are blended with the same amount
of talc (e.g. 2.5 to 5%).
More specifically, the polymer composition according to the present
invention is characterized by what is stated in the characterizing
part of claim 1.
The process according to the present invention for preparing
nucleated polypropylene compositions is characterized by what is
stated in the characterizing part of claim 9.
The present compositions can be used in any kind of polymer
articles. Particular advantages are obtained by applying the
compositions to the manufacture of moulded products, and products
prepared by blow moulding, stretch blow moulding, injection
moulding, compression moulding and sheet or film extrusion and pipe
or cable extrusion.
The invention achieves a number of considerable advantages. In
particular it can be noted that the addition of talc in amounts of
0.1 to 10 wt-% increases the stiffness of the propylene polymer
composition by up to 5%. Talc in polypropylene compositions gives
rise to higher tensile modulus than talc in standard PP copolymer.
The Heat Deflection Temperature (the HDT value) is also increased
by the addition of talk, and the HDT value increases more for the
present polypropylene compositions nucleated with a vinyl compound
than for standard PP. The crystallization temperature of the
present compositions is higher than for standard PP containing
corresponding amounts of talc and for polypropylene compositions
nucleated with a vinyl compound. Although the shrinkage of the
present compositions is somewhat higher than that of standard PP
containing talc it is still on an acceptable level and the present
invention provides a unique combination of excellent stiffness (up
to 1600 MPa or more), controlled shrinkage, faster crystallization
and high T.sub.cr giving good cyclus potential. In the present
context, faster crystallization is not necessarily related to
faster formation of single crystals but rather to the fact that
there are more crystals that fill the space faster.
Next, the invention will be more closely examined with the aid of
the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
The compositions of the present invention include a polymeric
component comprising a propylene polymer nucleated with vinyl
compounds together with a shrinkage-restricting component, talc. By
nucleating propylene polymers with vinyl compounds it is possible
to provide polypropylene having a higher degree of crystallinity, a
higher crystallization temperature, smaller crystallization size
and a greater crystallization rate. These kinds of compositions can
be used for the preparation of moulded products. They exhibit
improved physical properties.
The nucleation of the propylene polymers can be carried out by
modifying the polymerization catalyst with vinyl compounds and
using the modified catalyst for polymerization of propylene
optionally in the presence of comonomers to provide a propylene
polymer or copolymer containing about 0.0001 to 1% (calculated from
the weight of the composition) of a polymer comprising vinyl
compound units. Another approach for nucleating propylene polymers
comprises blending polypropylene with polymers containing vinyl
compound units.
For the purpose of the present invention "vinyl compounds" are
compounds having the formula I ##STR1##
wherein R.sub.1 and R.sub.2 together form a 5 or 6 membered
saturated or unsaturated or aromatic ring or they stand
independently for a lower alkyl comprising 1 to 4 carbon atoms.
The following specific examples of vinyl compounds can be
mentioned: vinyl cycloalkanes, in particular vinyl cyclohexane,
vinyl cyclopentane, vinyl-2-methyl cyclohexane and vinyl
norbornane, 3-methyl-1-butene, styrene, p-methyl-styrene,
3-ethyl-1-hexene or mixtures thereof. Vinyl cyclohexane (VCH) is a
particularly preferred monomer but, for example 3-methyl-1-butene
can be used as a monomer or comonomer to adjust the crystallisation
temperature.
For the purpose of the present invention "nucleated propylene
polymer" stands for a polymer having an increased and controlled
degree of crystallinity and preferably having a crystallization
temperature of more than 7.degree. C., preferably over 10.degree.
C. and in particular over 13.degree. C. of the T.sub.cr of the
corresponding non-nucleated polymer. Using MgCl.sub.2 -supported
high-yield Ziegler-Natta catalysts crystallization temperatures of
more than 120.degree. C., preferably over 124.degree. C. and in
particular over 126.degree. C. can be obtained. In compositions
containing colouring pigments having a nucleating effect,
particularly advantageous results are obtained by using polymers
having a crystallization temperature over 15.degree. C. higher than
that of the corresponding non-nucleated polymer (for a polymer
produced with the above-mentioned ZN-catalyst, 128.degree. C.).
According to a preferred embodiment of the present invention,
modification of the catalyst with by polymerizing a vinyl compound,
such as VCH, in the presence thereof is performed in an inert fluid
which does not dissolve the polymer formed (e.g. polyVCH). One
particularly preferred polymerization medium comprises a viscous
substance, in the following a "wax", such as an oil or a mixture of
an oil with a solid or semi-solid polymer (oil-grease). The
viscosity of such a viscous substance is usually 1,000 to 15,000 cP
at room temperature. The advantage of wax prepolymerization is that
the catalyst can be prepolymerized, stored and fed into the process
in the same media and catalyst wax preparation and
prepolymerization is performed in the same process device. Due to
the fact that no washing, drying, sieving and transferring thus are
needed, the catalyst activity is maintained (cf. Finnish Patent No.
95387). The present process is inexpensive because high catalyst
concentrations and high PP production capacities can be used. Also
the amount of waste is diminished because the medium used during
polymerization of the vinyl compound does not have to be
removed.
According to another preferred embodiment, the method for improving
the crystallinity and transparency of polypropylene by blending a
crystalline polypropylene with a vinyl cycloalkane polymer is
carried out by melt-kneading the crystalline polypropylene with the
crystal nucleating agent, compounding the crystal nucleating agent
with the crystalline polypropylene and melt kneading the mixture
during film formation, and compounding the master batch of the
crystal nucleating agent with the crystalline polypropylene.
The vinyl compound units of the blending and compounding process
can be derived from any of the units identified in the above
formula I in connection with the first embodiment of the
invention.
As catalyst any stereospecific catalyst for propylene
polymerization can be used, which is capable of catalyzing
polymerization and copolymerization of propylene and comonomers at
a pressure of 10 to 100 bar, in particular 25 to 80 bar, and at a
temperature of 40 to 110 .degree. C., in particular 60 to
100.degree. C. Ziegler-Natta as well as metallocene catalysts can
be used.
Generally, the Ziegler-Natta catalyst used in the present invention
comprises a catalyst component, a cocatalyst component, an external
donor, the catalyst component of the catalyst system primarily
containing magnesium, titanium, halogen and an internal donor.
Examples of suitable catalyst systems are described in, for
example, Finnish Patents Nos. 86866, 96615 and 88047 and 88048.
One particularly preferable catalyst, which can be used in the
present invention, is disclosed in FI Patent No. 88047. Another
preferred catalyst is disclosed in Finnish Patent Application No.
963707.
A catalyst system useful in the present process can be prepared by
reacting a magnesium halide compound with titanium tetrachloride
and an internal donor. The magnesium halide compound is, for
example, selected from the group of magnesium chloride, a complex
of magnesium chloride with a lower alkanol and other derivatives of
magnesium chloride. MgCl.sub.2 can be used as such or it can be
combined with silica, e.g. by absorbing the silica with a solution
or slurry containing MgCI.sub.2. The lower alkanol used can be
preferably methanol or ethanol, particularly ethanol.
The titanium compound used in the preparation of the procatalyst is
preferably an organic or inorganic titanium compound, having an
oxidation state of titanium of 3 or 4. Also other transition metal
compounds, such as vanadium, zirconium, chromium, molybdenum and
tungsten compounds can be mixed with the titanium compound. The
titanium compound usually is halide or oxyhalide, an organic metal
halide, or a purely metal organic compound, in which only organic
ligands have been attached to the transition metal. Particularly
preferable are the titanium halides, especially TiCl.sub.4.
Preferably the titanation is carried out in two or three steps.
The Ziegler-Natta catalyst used can also be an heterogeneous
unsupported TiCl.sub.3 based catalyst. This kind of catalysts are
typically solid TiCl.sub.5 in a delta crystalline form which are
activated with aluminium-chloride-alkyls, such as
diethylaluminiumchloride. The solid TiCl.sub.3 catalyst are
typically prepared by reduction of TiCl4 with aluminium-alkyls
and/or aluminium-chloride-alkyls, possibly combined with heat
treatment to maximise the desired delta crystalline form of
TiCl.sub.3. The performance, especially stereospecificity, of these
catalyst can be improved by using Lewis-bases (electron donors),
such as esters, ethers or amines.
The activity and stereospecificity of these heterogeneous
unsupported TiCl.sub.3 based catalysts are typically so low that
propylene polymers or copolymers prepared require purification from
catalyst residues and removal of some atactic non-crystalline
polymer.
The alkoxy group of the phthalic acid ester used comprises at least
five carbon atoms, preferably at least 8 carbon atoms. Thus, as the
ester can be used for example propylhexyl phthalate, dioctyl
phthalate, dinonyl phthalate, diisodecyl phthalate, di-undecyl
phthalate, ditridecyl phthalate or ditetradecyl phthalate.
The partial or complete transesterification of the phthalic acid
ester can be carried out e.g. by selecting a phthalic acid ester--a
lower alcohol pair, which spontaneously or with the aid of a
catalyst, which does not damage the procatalyst composition,
transesterifies the catalyst at an elevated temperatures. It is
preferable to carry out the transesterification at a temperature,
which lies in the range of 110 to 150.degree. C., preferably 120 to
140.degree. C.
The catalyst prepared by the method above is used together with an
organometallic cocatalyst and with an external donor. Generally,
the external donor has the formula IV
wherein R and R' can be the same or different and they stand for a
linear, branched or cyclic aliphatic, or aromatic group;
R" is methyl or ethyl; n is an integer 0 to 3; m is an integer 0 to
3; and n + m is 1 to 3.
The aliphatic groups in the meanings of R and R' can be saturated
or unsaturated. Linear C.sub.1 to C.sub.12 hydrocarbons include
methyl, ethyl, propyl, butyl, octyl and decanyl. As examples of
suitable saturated branched C.sub.1-8 alkyl groups, the following
can be mentioned: isopropyl, isobutyl, isopentyl, tert-butyl,
tert-amyl and neopentyl. Cyclic aliphatic groups containing 4 to 8
carbon atoms comprise, e.g., cyclopentyl, cyclohexyl, methyl
cyclopentyl and cycloheptyl.
A group of interesting donors is formed by strongly co-ordinating
donors which form relatively strong complexes with catalyst
surface, mainly with MgCl.sub.2 surface in the presence of
aluminium alkyl and TiCl.sub.4. The donor components are
characterised by a strong complexation affinity towards catalyst
surface and a sterically large and protective hydrocarbon (R').
Such external donors can be selected from the group consisting of
dicyclopentyl dimethoxysilane, diisopropyl dimethoxysilane,
di-isobutyl dimethoxysilane, and di-t-butyl dimethoxysilane.
An organoaluminum compound is used as a cocatalyst. The
organoaluminium compound is preferably selected from the group
consisting of trialkylaluminium, dialkyl aluminium chloride and
alkyl aluminium sesquichloride.
The metallocene catalyst comprises a metallocene/activator reaction
product impregnated in a porous support at maximum internal pore
volume. The catalyst complex comprises a ligand which is typically
bridged, and a transition metal of group IVA . . . VIA, typically a
metal halide, and aluminium alkyl. The ligands can belong to group
of heterocyclic substituted or unsubstituted compouns, e.g.
indocenes, naftenes, or any other bulky compound which can control
the stereoselectivity of the catalyst especially when ligands are
bridged together with silane or other chemical bond. The activator
is selected from a group in which are derivates of water and
aluminium alkyls e.g. trimethyl aluminium, triethyl aluminium, and
tri t-butyl aluminium, or another compound capable of activating
the complex. The metallocene/activator reaction product, a solvent
capable of dissolving it, and a porous support are brought into
mutual contact, the solvent is removed and the porous support is
impregnated with the metallocene/activator reaction product, the
maximum amount of which corresponds to the pore volume support, cf.
International PCT Application No. PCT/FI94/00499.
One typical structure of metallocene compound reactions is bridged
bis(2-R-4-R'-indenyl) M Cl.sub.2, wherein both R and R' are
aliphatic, cycloaliphatic or aromatic hydrocarbons having 1 to 18 C
atoms, R' is typically phenyl or naphthyl, and R is typically
methyl or ethyl. M is a transition metal, typically titanium,
zirconium or hafnium. R and R' may contain heteroatoms, such as
silicon, nitrogen, phosphorous or germanium. The bridge between the
indenyls is made from 1 to 3 atoms, such as carbon, silicon,
nitrogen, phosphorous or germanium. A typical bridge is
dimethylsilyl or ethyl. An example of such a metallocene compound
is dimethylsilyl-bis(2-methyl-4-phenyl-indenyl)zirconium
dichloride.
Following the modification of the catalyst with the vinyl compound
of the first preferred embodiment of the invention, the catalyst is
optionally prepolymerized with propylene and/or another 1-olefin to
provide a prepolymerized catalyst composition which is used for
polymerization of propylene optionally together with
comonomers.
The propylene homo- or copolymer can have a unimodal or bimodal
molar mass distribution. Thus, the equipment of the polymerization
process can comprise any polymerization reactors of conventional
design for producing propylene homo- or copolymers. For the purpose
of the present invention, "slurry reactor" designates any reactor,
such as a continuous or simple batch stirred tank reactor or loop
reactor, operating in bulk or slurry and in which the polymer forms
in particulate form. "Bulk" means a polymerization in reaction
medium that comprises at least 60 wt-% monomer. According to a
preferred embodiment the slurry reactor comprises a bulk loop
reactor. By "gas phase reactor" is meant any mechanically mixed or
fluid bed reactor. Preferably the gas phase reactor comprises a
mechanically agitated fluid bed reactor with gas velocities of at
least 0.2 m/sec.
Thus, the polymerization reactor system can comprise one or more
conventional stirred-tank slurry reactors, as described in WO
94/26794, or one or more gas phase reactors. Preferably the
reactors used are selected from the group of loop and gas phase
reactors and, in particular, the process employs at least one loop
reactor and at least one gas phase reactor. This alternative is
particularly suitable for producing bimodal polypropylene. By
carrying out the polymerization in the different polymerization
reactors in the presence of different amounts of hydrogen, the MWD
of the product can be broadened and its mechanical properties
improved. It is also possible to use several reactors of each type,
e.g. one loop reactor and two or three gas phase reactors or two
loop reactors and one gas phase reactor, in series.
In every polymerization step it is possible to use also comonomers
selected from the group of ethylene, propylene, butene, pentene,
hexene and alike as well as their mixtures.
In addition to the actual polymerization reactors used for
producing the propylene homo- or copolymer, the polymerization
reaction system can also include a number of additional reactors,
such as pre- and/or postreactors. The prereactors include any
reactor for prepolymerizing the catalyst with propylene and/or
other 1-olefins. The postreactors include reactors used for
modifying and improving the properties of the polymer product. All
reactors of the reactor system are preferably arranged in
series.
The gas phase reactor can be an ordinary fluidized bed reactor,
although other types of gas phase reactors can be used. In a
fluidized bed reactor, the bed consists of the formed and growing
polymer particles as well as still active catalyst come along with
the polymer fraction. The bed is kept in a fluidized state by
introducing gaseous components, for instance monomer on such
flowing rate which will make the particles act as a fluid. The
fluidizing gas can contain also inert carrier gases, like nitrogen
and also hydrogen as a modifier. The fluidized gas phase reactor
can be equipped with a mechanical mixer.
The gas phase reactor used can be operated in the temperature range
of 50 to 115.degree. C., preferably between 60 and 110.degree. C.
and the reaction pressure between 5 and 50 bar and the partial
pressure of monomer between 2 and 45 bar.
The pressure of the effluent, i.e. the polymerization product
including the gaseous reaction medium, can be released after the
gas phase reactor in order optionally to separate part of the
gaseous and possible volatile components of the product, e.g. in a
flash tank. The overhead stream or part of it is recirculated to
the reactor.
The propylene homo- or copolymer produced preferably has a MWD of
over 2 to 10 and a MFR.sub.2 in the range of 0.01 to 1000 g/10 min,
preferably 0.05 to 500 g/10 min, measured by ISO 1133, 230.degree.
C., 2.16 kg load.
In the second embodiment of the invention, wherein a uni- or
bimodal propylene homo- or copolymer is blended and compounded with
a polymer comprising vinyl compound units, the blending is carried
out as known in the art using said nucleating polymeric agent.
By means of both embodiments, a propylene homopolymer or copolymer
is produced having high stiffness, an increased overall degree of
crystallization and a crystallization temperature measured with DSC
of more than 7.degree. C., preferably over 10.degree. C. and in
particular 13.degree. C. higher than that of the corresponding
non-nucleated polymer. The degree of crystallization for the
propylene homopolymer is generally over 48%, often over 50 %, and
the elasticity modulus is about 2,000 MPa or more. The elasticity
modulus of heterophasic copolymers containing about 12 wt-% of a
rubbery component is about 1,500 MPa or more.
If desired, the polymerization product can be fed into a gas phase
reactor in which a rubbery copolymer is provided by a
(co)polymerization reaction to produce a modified polymerization
product. This polymerization reaction will give the polymerization
product properties of e.g. improved impact strength. The step of
providing an elastomer can be perfomed in various ways. Thus,
preferably an elastomer is produced by copolymerizing at least
propylene and ethylene into an elastomer. The conditions for the
copolymerization are within the limits of conventional EPM
production conditions such as they are disclosed, e.g., in
Encyclopedia of Polymer Science and Engineering, Second Edition,
Vol. 6, p.545-558. A rubbery product is formed if the ethylene
repeating unit content in the polymer lies within a certain range.
Thus, preferably, ethylene and propylene are copolymerized into an
elastomer in such a ratio that the copolymer contains from 10 to
70% by weight of ethylene units. In particular, the ethylene unit
content is from 30 to 50% by weight of the amorphous copolymer
propylene/ethylene elastomer. In other words, ethylene and
propylene are copolymerized into an elastomer in a molar ratio of
ethylene-to-propylene of 30/70 to 50/50. Polymers modified by
adding the rubbery copolymer in a gas phase reactor are typically
called polypropylene block copolymers or heterophasic
copolymers.
The amount of the nucleating polymeric agent is, in case of
propylene copolymers, about 0.0001 to 1 wt-%, and in case of
polypropylene blends about 0.0001 to 0.5 wt-%.
This nucleated polypropylene is then blended with talc in an amount
of 0.1 to 10 wt-%, preferably about 0.5 to 9 wt-%, in particular 1
to 8 wt-% (calculated from the total weight of the composition).
The talc used has a particle size in the range of of 0.01 to 100
.mu.m, preferably 0.1 to 10 .mu.m.
The present blends can be produced by methods known per se, e.g. by
mixing the polymer components with the talc in the desired weight
relationship using a batch or a continuous process. As examples of
typical batch mixers, the Banbury and the heated roll mill can be
mentioned. Continuous mixers are exemplified by the Farrel mixer,
the Buss co-kneader, and single- or twin-screw extruders.
A composition according to the invention containing some 1 to 8
wt-% talc exhibits at least about 10%, preferably about 12% to
about 25%, lesser shrinkage than the corresponding composition not
containing talc. This decreased shrinkage is manifested
particularly transverse to flow direction. Too high talc loading
will impair a further increase of stiffness and restrict shrinkage
below the lower tolerance of the moulds conventionally used for
processing in the melt stage.
As mentioned above, the mechanical properties of polymer
compositions according to invention are generally good to
excellent. Thus, with a loading of 1 to 8 wt-% talc, a polymer
composition of a heterophasic propylene copolymer containing about
12% of a rubbery component will have a stiffness (tensile modulus)
of over 1500 MPa and a HDT of over 106.degree. C. Generally, a
loading of 2.5% talc will increase the tensile modulus from, e.g.,
1440 MPa to 1600 MPa and a loading of 5% will further increase the
tensile modulus to 1750 MPa (tensile modulus measured by using ISO
527-2). Impact properties are not influenced by the addition of
talc in the range indicated, in particular if the amount of talc is
less than 5%.
The homopolymer or copolymer composition thus obtained can be used
for the manufacture of moulded articles, in particular articles
processed by blow moulding, thermoforming, injection moulding and
sheet or film extrusion, or pipe or cable extrusion. The
compositions of the invention are particularly suitable for pipes
and fitting for non-pressure sewage or pressure application, and
buffer tubes, e.g. for optical fibres, wherein the amount of
polymerized vinyl compound in the propylene polymer is less than
0.01 wt-%.
EXAMPLES
The following non-limiting examples illustrate the invention.
Example 1
Catalyst Modification with Polymerisation of Vinylcycloalkane
A high yield MgCl.sub.2 supported TiCl.sub.4 Ziegler-Natta catalyst
prepared according to Finnish patent Fl 88047 was dispersed into a
mixture of oil and grease (Shell Ondina Oil N 68 and Fuchs Vaseline
Grease SW in 3.2:1 oil/grease volume ratio). The titanium content
of the catalyst was 2.5 wt-%, and the concentration of the catalyst
in the oil/crease mixture was 189 g cat/dm.sup.3. Triethylaluminium
(TEAL) was added to the catalyst dispersion in a TEAL to titanium
mole ratio of 1.5. After that vinylcyclohexane (VCH) was added to
the reaction mixture, and the VCH to catalyst weight ratio was 1:1.
The reaction mixture was mixed at a temperature of 55.degree. C.
until the concentration of unreacted VCH in the reaction mixture
was 1000 ppm by weight.
Example 2
Copolymerisation of Propylene and Ethylene
The modified catalyst in the oil-grease mixture (catalyst mud)
obtained from Example 1 was continuously fed to process consisting
from a loop rector and a fluid bed gas phase rector together with
TEAL, dicyclopentyldimethoxysilane and propylene.
The TEAL and dicyclopentyldimethoxysilane at a weigth-to-weigth
ratio of 3.2 was contacted before mixing with the catalyst mud.
After that the mixture was flushed with propylene, containing the
desired amount of hydrogen as molecular weight regulating agent, to
a continuous stirred prepolymerisation reactor. After the
prepolymerisation, the reaction mixture together with additional
propylene and hydrogen was fed to a continuous loop reactor
operating at 68.degree. C. The resulted PP homopolymer-propylene
slurry containing the catalyst was continuously recovered from the
loop reactor to a flashing unit where the liquid propylene was
vaporised and the remaining solid polymer particles, containing the
active modified catalyst, was further fed to a continuous fluidised
bed gas phase reactor where a rubbery propylene ethylene copolymer
for impact modification was produced. The gas phase reactor was
operated at 77.degree. C. The desired amount of propylene and
ethylene was continuously fed to the reactor, and the molecular
weight of the copolymer produced was controlled with desired amount
of hydrogen. The final polymer was continuously recovered from the
gas phase reactor. After purging the unreacted monomers, the
required stabilisers and other additives were added and the polymer
powder was pelletised with an extruder.
The final polymer had an MFR.sub.2 of 15 g/10 min, and an ethylene
content of 8 wt-%. The amount of polymer precipitated with acetone
(AM) from solubles in 23.degree. C. xylene (XS) was 13.9 wt-%,
which corresponds to the amount of rubbery copolymer made in the
gas phase reactor. The MFR.sub.2 of the polymer recovered from the
loop reactor was 20 g/10 min. The ethylene content of the polymer
precipitated with acetone from solubles in 23.degree. C. xylene was
37.4 wt-%. The polymer solubles in xylene at 25.degree. C. were
measured by dissolving the polymer in xylene at 135.degree. C., and
allowing the solution to cool to 25.degree. C. and filtering then
the insoluble part out. The amorphous part, AM, was measured by
separating the above xylene soluble fraction and precipitating the
amorphous part with acetone.
Example 3
Blending of Nucleated PP with Talc
The nucleated polypropylene prepared according to Example 2 was
blended with talc and compounded in a extruder. The stiffness of
the present compositions were compared with those of a standard
nucleated PP copolymer. The nucleation agent of the standard
copolymer was talc (<0.5%) or Sodium Benzoate (<0.1%).
Tensile modulus were measured according to ISO 527-2:
Shrinkage Standard PP polymer Tensile modulus 1,400 MPa 1.47%
Standard PP copolymer + Tensile modulus 1,420 MPa 1.38% 3% talc
Copolymer of Example 2 Tensile modulus 1,400 MPa 1.70% Copolymer of
Example 2 + Tensile modulus 1,600 MPa 1.59% 3% talc
Shrinkage is measured from open top containers according to
Borealis "Injection moulding application method 4".
The results show that by blending a copolymer nucleated with
polymerized vinyl compounds and talc a surprising increase in the
tensile modulus can be obtained; the propylene copolymer of Example
2 responded to talc with much higher modulus than the standard PP
copolymer. The shrinkage values show that the invention provides a
unique combination of excellent stiffness and controlled
shrinkage.
Example 4
The Effect on HDT and Tc
The nucleated polypropylene prepared according to Example was
blended with talc and compounded in a extruder. The stiffness of
the present compositions were compared with those of a standard
nucleated PP copolymer. The nucleation agent of the standard
copolymer was talc (<0.5%) or Sodium Benzoate (<0.1%).
Heat Deflection Temperature (HDT) was measured according to ISO-
75-2 (method B/0.45 MPa).
Temperature of crystallisation was measured with differential
scanning calorimeter (DSC) at a cooling rate of 10.degree.
C./min.
Standard PP copolymer HDT 100.degree. C. T.sub.cr 123.degree. C.
Standard PP copolymer + 3% talc HDT 104.degree. C. T.sub.cr
127.degree. C. Copolymer of Example 2 HDT 103.degree. C. T.sub.cr
129.degree. C. Copolymer of Example 2 + 3% talc HDT 109.degree. C.
T.sub.cr 131.degree. C.
The above results clearly show that, when blended with talc,
polymers nucleated with polymerized vinyl compounds have better
properties than the pure nucleated PP polymer and the standard PP
copolymer blended 3% talc.
Thus, the above results indicate that a synergistic effect on heat
deflection temperature (HDT) and temperature of crystallisation
(Tcr) can be obtained by blending polymerically nucleated PP and
talc.
* * * * *